The invention relates to improvements in torsional vibration damping devices, especially to improvements in damping devices which can be installed in the clutch plates or clutch discs of frictional clutches for motor vehicles.
Published British patent application No. A-20 80 488 discloses a clutch plate having a torsional vibration damping device with a first damper and a second or main damper. The first damper employs a set of relatively weak coil springs which oppose angular movements of an input member and an output member relative to each other, and the main damper employs stronger coil springs which oppose angular movements of an input member and an output member relative to each other. The output means of the clutch plate is a hub which can transmit torque to the input shaft of a change-speed transmission in the power train between the internal combustion engine and the wheels of a motor vehicle.
A drawback of the clutch plate which is disclosed in the published British patent application is that the first damper must be preassembled at the outer side of one of two disc-shaped walls forming part of input means of the clutch plate. The first damper comprises a large number of parts including a pair of spaced-apart plate-like guides for a flange which is disposed between the guides. The guides must be affixed to one of the walls by a set of rivets. This contributes to the initial cost of the clutch plate. Moreover, the just discussed clutch plate is bulky (particularly in the axial direction of the hub) which creates problems when it is to be used in the friction clutch between the crankshaft of the engine and the input shaft of the change-speed transmission in a compact motor vehicle.
Published French patent application Ser. No. 2 503 295 of Muller discloses a torsion damping assembly wherein the first damping stage is disposed radially inwardly of and is surrounded by the second damping stage, i.e., the two damping stages are in radial alignment with each other. Such torsion damping assemblies are quite bulky (especially as considered in the radial direction of the clutch plate), namely even bulkier than the torsion damping assemblies of the type disclosed in the published British patent application No. A-20 80 488.